Personal income tax is a tax on the income of an individual. Insurance premiums are deductions to the tax office for the accumulation of pensions and free appointments at the clinic.
If an entrepreneur cooperates with an individual without the status of self-employed or registered individual entrepreneur, the responsibility of paying personal income tax and contributions passes to him. An obligation in a contract cannot be canceled. Even if the person himself agrees to it.
If you neglect your duty, the tax office will fine you under Art. 123 of the Tax Code of the Russian Federation - for the tax itself, and under Art. 119 - for an unsubmitted report. And, of course, he will collect the debt with a penalty.